粮油食品之家

简介

　　淀粉是葡萄糖的高聚体，水解到二糖阶段为麦芽糖，完全水解后得到葡萄糖。淀粉有直链淀粉和支链淀粉两类。直链淀粉含几百个葡萄糖单元，支链淀粉含几千个葡萄糖单元。在天然淀粉中直链的约占22％～26％，它是可溶性的，其余的则为支链淀粉。当用碘溶液进行检测时，直链淀粉液呈显蓝色，而支链淀粉与碘接触时则变为红棕色。 　　淀粉是植物体中贮存的养分，存在于种子和块茎中，各类植物中的淀粉含量都较高，大米中含淀粉62％～86％，麦子中含淀粉57％～75％，玉蜀黍中含淀粉65％～72％，马铃薯中则含淀粉12％～14％。淀粉是食物的重要组成部分，咀嚼米饭等时感到有些甜味，这是因为唾液中的淀粉酶将淀粉水解成了二糖--麦芽糖。食物进入胃肠后，还能被胰脏分泌出来的唾液淀粉酶水解，形成的葡萄糖被小肠壁吸收，成为人体组织的营养物。支链淀粉部分水解可产生称为糊精的混合物。糊精主要用作食品添加剂、胶水、浆糊，并用于纸张和纺织品的制造(精整)等。淀粉的分类 淀粉可根据分子结构分为直链淀粉和支链淀粉，根据来源分为玉米淀粉、小麦淀粉、马铃薯淀粉、甘薯淀粉等。

淀粉的性质

    淀粉是葡萄糖的高聚体，水解到二糖阶段为麦芽糖，完全水解后得到葡萄糖。淀粉有直链淀粉和支链淀粉两类。直链淀粉含几百个葡萄糖单元，支链淀粉含几千个葡萄糖单元。在天然淀粉中直链的约占22％～26％，它是可溶性的，其余的则为支链淀粉。当用碘溶液进行检测时，直链淀粉液呈显蓝色，而支链淀粉与碘接触时则变为红棕色。

    淀粉是植物体中贮存的养分，存在于种子和块茎中，各类植物中的淀粉含量都较高，大米中含淀粉62％～86％，麦子中含淀粉57％～75％，玉蜀黍中含淀粉65％～72％，马铃薯中则含淀粉12％～14％。淀粉是食物的重要组成部分，咀嚼米饭等时感到有些甜味，这是因为唾液中的淀粉酶将淀粉水解成了二糖--麦芽糖。食物进入胃肠后，还能被胰脏分泌出来的淀粉酶水解，形成的葡萄糖被小肠壁吸收，成为人体组织的营养物。支链淀粉部分水解可产生称为糊精的混合物。糊精主要用作食品添加剂、胶水、浆糊，并用于纸张和纺织品的制造(精整)等。

         淀粉分解图

淀粉的应用

　　 淀粉的应用领域包括；造纸业、纺织业、食品加工业、胶粘剂生产以及其它领域。

食品加工业

    在食品工业中，许多淀粉都用于焙烤特殊食品所需。例如瑞士和德国风味的面包，薄脆饼干，未发酵面包等。它同时也可作为汤和肉汁的增稠剂，淀粉制成颗粒作为“布丁”，其效果类似于通常用木薯淀粉制作的布丁。预制胶状的马铃薯淀粉已大量用作“速煮”布丁。

    淀粉可作为制作造型糖果的成形剂，例如，一种密线豆形的胶质软粒，桔形糖片和液滴形软胶。作为稠化剂以增加焦糖和果汁软糖的光滑性和稳定性。 淀粉还作为一种粉剂与粉末糖(棉白糖)混合，制作果胶糖，口香糖等。

    绿豆淀粉：来自豆科植物绿豆的种子，用于制作绿豆粉丝、绿豆凉粉，但跟绿豆直接磨成的用来做绿豆糕的绿豆面不同。玉米淀粉：又称粟粉，来自禾本科植物玉米的种子，掺入面粉中可以降低面粉的筋度，在奶油布丁馅、菠萝馅等派、蛋挞、馅饼等西点的馅料中起粘稠作用，也是冰淇淋的原料之一。玉米淀粉是玉米中提取出来的淀粉成分，呈白色，与玉米粒直接磨成的黄色玉米面不同。马铃薯淀粉：来自茄科植物马铃薯(土豆、洋芋)的块茎。马蹄淀粉：来自莎草科植物荸荠(又称马蹄)的球茎，是马蹄糕的原料。莲藕淀粉：就是藕粉，来自睡莲科植物荷的根和茎，可以直接用开水冲食。

造纸业

    在造纸业中，淀粉或变性淀粉主要四种用途：⑴.打浆机上胶，在薄纸成形之前，将纤维组织凝结在一起。⑵.桶上胶，浸透稀胶液，预形成薄纸。⑶.轧光机上胶，上光整修。⑷.表面上胶，作为一个任意选择的步骤，作高级光滑纸的上胶：在制作皱纹、波纬．纤维胶合纸板箱时淀粉和糊精同样可用来组合和糊粘纸板。

    另有一种淀粉制品，是将蒸煮过的马铃薯淀粉乳置于滚筒式干燥器中干燥成糊片，然后将糊片碾碎成粉末即成。这种制品易溶于冷水中，使用在造纸工业的打浆机上胶作业中取得了显著的效果，在打浆机上胶中，人们都喜欢用可溶性马铃薯淀粉或糊，而不愿用其它淀粉制作的产品，因为可溶马铃薯淀粉糊对纤维具有很大的粘性和粘聚强度。此外，这些特性很少影响造纸过程中矾的添加，矾是造纸过程中主要辅料，它所具有的酸性对大多数其他淀粉糊的特性是不利的。

    淀粉还用在纸张上光方面。例如制造用于期刊外光滑纸，这里，马铃薯淀粉粉末对于提高白颜抖和枯土的凝固强度都是非常有利的，可以说、在纸的上光方面，淀粉已经很大程度地代替了酪蛋白的法用。

纺织业

    在纺织工业中，淀粉主要是用于棉纱、毛织物和纺人造丝织物的上浆，经纱上浆就是将沿纺织机纵向运动的纬线浸渍在一个装有淀粉糊的热锅内，从浴锅出来，经上浆后的纬线在一个热滚筒内迸行干燥制待，经纱上浆的作用就是将纬线表面的一些疏松的纤维紧紧地粘结，以增强和保持经纱在编织时的耐摩性，高支经纱（即含很多单支纤维纺成豹一股纱）上浆通常是较困难的，因为纤维之间的缝隙很小，浆液不易渗透，最后形成一层薄膜牢固的粘附在纱上。因此，增强了纱的强度和耐摩性。已经知道，相对于其他淀粉，马铃薯淀粉膜具有较高的韧性和柔性，因此，经马铃薯淀粉上浆的纱比其他用玉米淀粉上浆的纱具有可在较低湿度环境中纺织的优点。

     在人造纱的纺织中，用淀粉上浆能获得光洁的制品。谷物淀粉糊常含有较大的胶凝料粒子，易粘附在纱上，凝胶后，常会钩住纺织机而引起断线。而用马铃薯淀粉上浆的纱不但光滑而且较容易地在上浆后除去剩余浆液。特别是停料后，相对于谷物淀粉，马铃薯淀粉的胶凝的“老化”或“凝沉”作用的趋势较小、作为凝胶剂这是一个优点。经用马铃薯淀粉上浆的纱具有另一个优点是染色后能得到鲜艳的色泽。

    缝纫用棉线的精加工类似于经纱上浆、线被浸渍在一个浴锅内。然后精梳：这里使用的业多时马铃薯淀粉上浆。

    当淀粉作为纺织品印花用糊的增稠剂时，在染桶里它所能显示的颜色强度是不显著的，但具有作精梳上光剂的优良特性。用淀粉精梳的棉纺品具有一个良好的手感（用手抚摸时）和光滑的表面。


胶粘剂生产

    生产胶粘剂过程中，通常是将淀粉经化学和物理处理后制成变性淀粉后而改变它的粘性并增加胶粘性。虽然用作胶粘剂的一些淀粉是低粘度淀粉和氧化性淀粉，但都以糊精的形式使用。糊精是将淀粉在一种酸催化剂作用下加热而制成。通常，用根部和块茎植物的薯类淀粉制成的薄膜糊精比谷物淀粉糊精具有更大的柔性和抗裂外。淀粉糊精有许多用途，根据它们的特性可制成人们所称心的东西。例：砂纸．砂布、装饰和地毯上浆中的粘合剂，这些东西制造都需要具有高度胶粘性的糊精，以形成一个可塑而有后效的胶膜。在涂胶后显示再湿性方面，淀粉糊精膜同样受人们注意，这些特性是作为涂胶邮票，标签，封皮、胶带的涂胶剂可需的。

   总体来说，淀粉具有不溶于水、水中分散、60～70摄氏度溶胀的特点。常被用作稀释剂、粘合剂、崩解剂，并可用来制备糊精和淀粉浆。　　

    1用作稀释剂(Diluents)：稀释剂(或称为填充剂，Fil1ers)的主要作用是用来填充片剂的重量或体积，以便于制剂成型和分剂量，从而便于压片；常用的填充剂有淀粉类、糖类、纤维素类和无机盐类等。　　以淀粉作为稀释剂时，比较常用的是玉米淀粉，它的性质非常稳定，与大多数药物不起作用，价格也比较便宜，吸湿性小、外观色泽好，在实际生产中，常与可压性较好的糖粉、糊精混合使用，这是因为淀粉的可压性较差，若单独使用，会使压出的药片过于松散。

　　2用作粘合剂(Adhesives)：某些药物粉末本身不具有粘性或粘性较小，需要加入淀粉浆等粘性物质，才能使其粘合起来，这时所加入的粘性物质就称为粘合剂。　　淀粉浆（俗称淀粉糊）是片剂中最常用的粘合剂，常用8%～15%的浓度，并以10%淀粉浆最为常用；若物料可压性较差，可再适当提高淀粉浆的浓度到20%，相反，也可适当降低淀粉浆的浓度，如氢氧化铝片即用5%淀粉浆作粘合剂。淀粉浆的制法主要有煮浆和冲浆两种方法，都是利用了淀粉能够糊化的性质。所谓糊化(Gelatinization)是指淀粉受热后形成均匀糊状物的现象(玉米淀粉完全糊化的温度是77℃)。糊化后，淀粉的粘度急剧增大，从而可以作为片剂的粘合剂使用。具体说来，冲浆是将淀粉混悬于少量(1～1.5倍)水中，然后根据浓度要求冲入一定量的沸水，不断搅拌糊化而成；煮浆是将淀粉混悬于全部量的水中，在夹层容器中加热并不断搅拌(不宜用直火加热，以免焦化)，直至糊化。因为淀粉价廉易得且粘合性良好，所以凡在使用淀粉浆能够制粒并满足压片要求的情况下，大多数选用淀粉浆这种粘合剂。

　　3用作崩解剂(Disintegrants)：崩解剂是使片剂在胃肠液中迅速裂碎成细小颗粒的物质，除了缓(控)释片以及某些特殊用途的片剂以外，一般的片剂中都应加入崩解剂。由于它们具有很强的吸水膨胀性，能够瓦解片剂的结合力，使片剂从一个整体的片状物裂碎成许多细小的颗粒，实现片剂的崩解，所以十分有利于片剂中主药的溶解和吸收。　　干淀粉是一种最为经典的崩解剂，含水量在8%以下，吸水性较强且有一定的膨胀性，较适用于水不溶性或微溶性药物的片剂，但对易溶性药物的崩解作用较差，这是因为易溶性药物遇水溶解产生浓度差，使片剂外面的水不易通过溶液层面透入到片剂的内部，阻碍了片剂内部淀粉的吸水膨胀。在生产中，一般采用外加法、内加法或“内外加法”来达到预期的崩解效果。　　淀粉作为片剂崩解剂的缺点：首先，淀粉的可压性不好，用量多时，可影响片剂的硬度。其次，淀粉的流动性不好，外加淀粉过多会影响颗粒的流动性。

　　4制备糊精：糊精 (C6H10O5)x,由淀粉经酸或热处理或经a-淀粉酶作用而成的不完全水解的产物，可用于制备各种液体或固体的胶粘剂。淀粉遇碘变蓝的特性　　淀粉具有遇碘变蓝的特性，这是由淀粉本身的结构特点决定的。淀粉是白色无定形的粉末，由10％～30％的直链淀粉和70％～90％的支链淀粉组成。溶于水的直链淀粉借助分子内的氢键卷曲成螺旋状。如果加入碘液，碘液中的碘分子便嵌入到螺旋结构的空隙处，并且借助范德华力与直链淀粉联系在一起，形成了一种络合物。这种络合物能够比较均匀地吸收除了蓝光以外的其他可见光(波长范围为400～750 nm)，从 而使淀粉溶液呈现出蓝色来。

烹饪如何用淀粉

　　淀粉也就是俗称的“芡”，为白色无味粉末，主要从玉米、甘薯等含淀粉多的物质中提取。可直接食用，也可用于酿酒，同时还是经常出入筵席的烹调辅料，在烹饪中具有无可替代的效用。勾芡一般用两种方法。一种是淀粉汁加调味品，俗称“对汁”，多用于火力旺，速度快的熘、爆等方法烹调的菜肴。另一种是单纯的淀粉汁，又叫“湿淀粉”，多用于一般的炒菜。浇汁也是勾芡的一种，又称为薄芡、琉璃芡，多用于煨、烧、扒及汤菜。根据烹调方法及菜肴特色，大体上有以下几种芡汁用法： 　　包芡一般用于爆炒方法烹调的菜肴。粉汁最稠，目的是使芡汁全包到原料上，如鱼香肉丝、炒腰花等，都是用包芡，吃完菜后，盘底基本不留卤汁。 　　糊交一般用于熘、滑、焖、烩方法烹制的菜肴。粉汁比包芡稀，用处是把菜肴的汤汁变成糊状，达到汤菜融合，口味滑柔，如：糖醋排骨、糖醋鲤鱼等。 　　流芡粉汁较稀，一般用于大型或整体的菜肴，其作用是增加菜肴的滋味和光泽。一般是在菜肴装盘后，再将锅中卤汁加热勾芡，然后浇在菜肴上，一部分沾在菜上，一部分呈琉璃状态，食后盘内可剩余部分汁液。 　　奶汤芡是芡汁中最稀的，又称薄芡。一般用于烩烧的菜肴，如：麻辣豆腐、虾仁锅巴等。目的是使菜肴汤汁加浓一点而达到色美味鲜的要求。 　　勾芡，就是在菜肴接近成熟时，将调匀的淀粉汁淋在菜肴上或汤汁中，使菜肴汤汁浓稠，并粘附或部分粘附于菜肴之上的过程。袁牧在《随园食单·用纤须知》中说：“俗名豆粉为纤者，即拉船用纤也。须顾名思义。因治肉者要作团而不能合，要作羹而不能腻，故以粉牵合之。煎炒之时，虑肉贴锅，必至焦老，故用粉以持之。此纤义也。”芡是由纤转音而来，所以现在通称之为“勾芡”。

　　由于菜肴各自不同的风味要求，勾芡主要有以下作用：

 　　1增加汤汁的粘稠度。菜肴在加热过程中，原料中的汁液会向外流，与添加的汤水及液体调味品便融合形成了卤汁。一般炒菜中的卤汁较稀薄，不易粘附在原料表面，成菜后会产生“不入味”的感觉。勾芡后，芡汁的糊化作用增加了卤汁的粘稠度，使卤汁能够较多地附着在菜肴之上，提高了人们对菜肴滋味的感受。

 　　2芡汁勾入菜肴中，芡汁会紧包原料，从而制止了原料内部水分外溢，这样做既保持了菜肴鲜香滑嫩的风味特点，又使菜肴形体饱满而不易散碎。

 　　3勾芡后，由于淀粉的糊化，具有透明的胶体光泽，能将菜肴与调味色彩更加鲜明地反映出来，使菜肴色泽更加光亮美观。

 　　4菜肴勾芡后能使汤汁变浓稠，可减缓原料内部热量的散发，使菜肴具有保温性，延长了菜肴的冷却时间，有利于食客进食热菜肴。

　　不过用好淀粉可是大有学问，一般中国烹调中大致有三种用淀粉的方法，就是挂糊、上浆和勾芡。挂糊就是下锅前在原料上加干淀粉；上浆就是下锅前在原料上加水淀粉；勾芡就是在起锅前加水淀粉使菜肴的汤变稠。那么到底什么样的菜肴，如何用淀粉才合适呢？　　如果您是要爆、炒、熘菜肴，芡汁一定要够浓，这样才能裹住原料，不会让汤汁四溢；如果您是扒、烩、烧菜肴，浓度要略底但仍要属浓芡，这样汤汁既能呈流动感又能与原料合为一体；如果您是做汤汁流动的菜肴，可施薄芡，只要汤的浓度达到您需要的程度就可以了，太浓会糊，太稀又会显得寡淡。　　用淀粉时控制油温十分重要。烹调上浆的菜肴时，油温太高，淀粉容易黏结成块；油温太低，淀粉容易与原料脱离，也就失去了保护层的作用，所以最好在有少量油烟出现时下锅；而在挂糊煎炸时，追求的是焦黄松脆，这时就需要油温高一些，油烟大量出现时下锅为最佳时机；勾芡时也要掌握好时机，太早容易发糊黏锅，太晚又会分布不匀，这就需要我们见机行事了。

Starch
From Wikipedia, the free encyclopedia

Starch, CAS# 9005-25-8, chemical formula (C6H10O5)n is a polysaccharide carbohydrate consisting of a large number of glucose monosaccharide units joined together by glycosidic bonds. All plant seeds and tubers contain starch which is predominantly present as amylose and amylopectin. Depending on the plant, starch generally contains 20 to 25 percent amylose and 75 to 80 percent amylopectin. Starch is also a carbohydrate that gives us energy.[1].

Etymology
Starch derived from Middle English sterchen, meaning to stiffen, which is appropriate since it can be used as a thickening agent when dissolved in water and heated. In several languages, starch is known as sago or sagu; consequently, in English sago now refers to several different starches (see Sago (disambiguation)). Starch is basically long chains of glucose molecules.

Sources of starch
 
Granules of wheat starch, stained with iodine, photographed through a light microscopeStarch is a white powder, and depending on the source, may be tasteless and odorless. Microscopically, starch grains are fine crystals or lumps; the precise form of these grains varies within the plant kingdom. Today, commercial starches include cornstarch, arrowroot, potato starch, sago and tapioca. Historically they included Florida arrowroot.

Uses
Starch in its basic refined form is used in cooking to thicken foods such as sauces. In industry, it is used in the manufacturing of adhesives, paper, textiles and as a mold in the manufacture of sweets such as wine gums and jelly beans. It is also used in the form of flakes, sticks, and pearls (tapioca and sago).

Food
Starch is by far the most consumed polysaccharide in the human diet. Traditional staple foods such as cereals, roots and tubers are the main source of dietary starch.

The technical term for a colorless, tasteless, odorless, and edible starch is a fecula.

Starch is often found in the fruit, seeds, rhizomes, and tubers, of plants, and is the major source of energy in these food items. The major resources for starch production and consumption worldwide are rice, wheat, corn, and potatoes. Fresh chestnut has twice as much starch as potato. As the chestnut ripens, some of its starch is gradually converted into sugars.[2] Cooked foods containing starches include boiled rice, various forms of bread and noodles (including pasta).

As an additive for food processing, arrowroot and tapioca are commonly used as well. Commonly used starches around the world are: arracacha, buckwheat, banana, barley, cassava, kudzu, oca, sago, sorghum, regular household potatos, sweet potato, taro and yams. Edible beans, such as favas, lentils and peas, are also rich in starch.

When a starch is pre-cooked, it can then be used to thicken cold foods. This is referred to as a pregelatinized starch. Otherwise starch requires heat to thicken, or "gelatinize."[vague]The actual temperature depends on the type of starch.

A modified food starch undergoes one or more chemical modifications, which allow it to function properly under high heat and/or shear frequently encountered during food processing. Food starches are typically used as thickeners and stabilizers in foods such as puddings, custards, soups, sauces, gravies, pie fillings, and salad dressings, but have many other uses.

The modified starches are coded according to the International Numbering System for Food Additives (INS) :

1401 Acid-treated starch

1402 Alkaline treated starch

1403 Bleached starch

1404 Oxidized starch

1405 Starches, enzyme-treated

1410 Monostarch phosphate

1411 Distarch glycerol

1412 Distarch phosphate esterified with sodium trimetaphosphate

1413 Phosphated distarch phosphate

1414 Acetylated distarch phosphate

1420 Starch acetate esterified with acetic anhydride

1421 Starch acetate esterified with vinyl acetate

1422 Acetylated distarch adipate

1423 Acetylated distarch glycerol

1440 Hydroxypropyl starch

1442 Hydroxypropyl distarch phosphate

1443 Hydroxypropyl distarch glycerol

1450 Starch sodium octenyl succinate

Resistant starch is starch that escapes digestion in the small intestine of healthy individuals.

Plants use starch as a way to store excess glucose, and thus also use starch as food during mitochondrial oxidative phosphorylation.

Commercial applications
 
Starch adhesivePapermaking is the largest non-food application for starches globally, consuming millions of metric tons annually. In a typical sheet of copy paper for instance, the starch content may be as high as 8%. Both chemically modified and unmodified starches are used in papermaking. In the wet part of the papermaking process, generally called the “wet-end”, starches are chemically modified to contain a cationic or positive charge bound to the starch polymer, and are utilized to associate with the anionic or negatively charged paper fibers and inorganic fillers.

These cationic starches impart the necessary strength properties for the paper web to be formed in the papermaking process (wet strength), and to provide strength to the final paper sheet (dry strength). In the dry end of the papermaking process the paper web is rewetted with a solution of starch paste that has been chemically, or enzymatically depolymerized. The starch paste solutions are applied to the paper web by means of various mechanical presses (size press). The dry end starches impart additional strength to the paper web and additionally provide water hold out or “size” for superior printing properties.

Corrugating glues are the next largest consumer of non-food starches globally. These glues are used in the production of corrugated fiberboard (sometimes called corrugated cardboard), and generally contain a mixture of chemically modified and unmodified starches that have been partially gelatinized to form an opaque paste. This paste is applied to the flute tips of the interior fluted paper to glue the fluted paper to the outside paper in the construction of cardboard boxes. This is then dried under high heat, which provides the box board strength and rigidity.

Another large non-food starch application is in the construction industry where starch is used in the gypsum wall board manufacturing process. Chemically modified or unmodified starches are added to the stucco containing primarily gypsum. Top and bottom heavyweight sheets of paper are applied to the formulation and the process is allowed to heat and cure to form the eventual rigid wall board. The starches act as a glue for the cured gypsum rock with the paper covering and also provide rigidity to the board.

Clothing starch or laundry starch is a liquid that is prepared by mixing a vegetable starch in water (earlier preparations also had to be boiled), and is used in the laundering of clothes. Starch was widely used in Europe in the 16th and 17th centuries to stiffen the wide collars and ruffs of fine linen which surrounded the necks of the well-to-do. During the 19th century and early 20th century, it was stylish to stiffen the collars and sleeves of men's shirts and the ruffles of girls' petticoats by applying starch to them as the clean clothes were being ironed. Aside from the smooth, crisp edges it gave to clothing, it served practical purposes as well. Dirt and sweat from a person's neck and wrists would stick to the starch rather than fibers of the clothing, and would easily wash away along with the starch. After each laundering, the starch would be reapplied. Today the product is sold in aerosol cans for home use.

Starch is also used to make some packing peanuts, and some dropped ceiling tiles.

Printing industry - in the printing industry food grade starch is used in the manufacture of anti-set-off spray powder used to separate printed sheets of paper to avoid wet ink being set off. Starch is also used in the manufacture of glues[4] for book-binding.

Hydrogen production - Starch can be used to produce Hydrogen.

Oil exploration - starch is used as to adjust the viscosity of drilling fluid which is used to lubricate the drill head in (mineral) oil extraction.

Body powder - Powdered corn starch is used as a substitute for talcum powder in many health and beauty products.

Use as a mold
Gummed sweets such as jelly beans and wine gums are not manufactured using a mold in the conventional sense. A tray is filled with starch and leveled. A positive mold is then pressed into the starch leaving an impression of 1000 or so jelly beans. The mix is then poured into the impressions and then put into a stove to set. This method greatly reduces the number of molds that must be manufactured.

Starch can be modified by addition of some chemical forms to be a hard glue for paper work , some of those forms are Borax , Soda Ash , which mixed with the starch solution at 50-70C to gain a very good adhesive, Sodium Silicate can be added to reinforce this formula.

Tests
Iodine solution is used to test for starch. A bluish-black color indicates the presence of iodine in the starch solution. It is thought that the iodine fits inside the coils of amylose.[6] A 0.3% w/w solution is the standard concentration for a dilute starch indicator solution. It is made by adding 4 grams of soluble starch to 1 litre of heated water; the solution is cooled before use (starch-iodine complex becomes unstable at temperatures above 35 °C). This complex is often used in redox titrations: in presence of an oxidizing agent the solution turns blue, in the presence of reducing agent, the blue color disappears because triiodide (I3−) ions break up into three iodide ions, disassembling the complex.

Under the microscope, starch grains illuminated from behind with polarized light show a distinctive Maltese cross effect (also known as extinction cross and birefringence).

Starch derivatives
Starch can be hydrolyzed into simpler carbohydrates by acids, various enzymes, or a combination of the two. The extent of conversion is typically quantified by dextrose equivalency (DE), which is roughly the fraction of the glycoside bonds in starch that have been broken. Food products made in this way include:

Maltodextrin, a lightly hydrolyzed (DE 10–20) starch product used as a bland-tasting filler and thickener.
Various corn syrups (DE 30–70), viscous solutions used as sweeteners and thickeners in many kinds of processed foods.
Dextrose (DE 100), commercial glucose, prepared by the complete hydrolysis of starch.
High fructose syrup, made by treating dextrose solutions with the enzyme glucose isomerase, until a substantial fraction of the glucose has been converted to fructose. In the United States, high fructose corn syrup is the principal sweetener used in sweetened beverages because fructose tastes sweeter than glucose, and less sweetener may be used.